[Amps] SB-220 6 meter conversion parasites

[Colin Lamb]

Without any other more sophisticated instruments, use a grid dip meter in absorption mode to learn what frequency the oscillation is.  Knowing that, you can solve the problem.  Perhaps it is near 50 MHz - in which case it is not a parasitic but simply feedback helping you to create a 50 MHz oscillator.  You may have a number of things that may be working together to create the oscillator:

1. grid not grounded
2. parasitic network not effective
3. input circuit not effective
4. output circuit may have too much stray inductance

Electrons really do not care what your intent is.  They are somewhat like a rattlesnake.  Kept in their own space, they cause no problems.  But let them out to wander around and they are likely to bite.  

73,  Colin  K7FM